Field of the Invention
The present disclosure relates to a circuit for improving a power factor and a charger for vehicles employing the circuit.
Discussion of the Related Art
Pollution-free and eco-friendly vehicles have recently become prominent. Such an eco-friendly vehicle has been essentially using a converter for charging a battery with a high voltage. The converter requires a power factor correction (PFC) circuit intended to increase a voltage and improve a power factor.
The PFC circuit requires a high rated voltage and a high capacity, and thus an electrolytic capacitor, which is most advantageous in terms of packaging at the time of design, has been used.
The electrolytic capacitor may satisfy a high rated voltage and a high capacity while the electrolytic capacitor is small. However, the electrolytic capacitor has a dielectric of a liquid substance, and thus degradation of reliability due to current stress (current ripple) has emerged as a serious problem.
For example, an electrolyte evaporates when the electrolytic capacitor is exposed to a great amount of ripple current. As a result, the dielectric cannot properly operate, which leads to decrease in capacity of the capacitor.
Further, the above-described converter uses high-voltage alternating current (AC) power as an input, and is involved with high frequency switching. Thus, the converter has been significantly weak in terms of electromagnetic compatibility (EMC).
When countermeasures for EMC cannot be established, marketability of a whole vehicle in addition to the converter as a single unit may be degraded. Seriously, a risk of dissatisfaction with vehicle regulations may be entailed.